When Fernando Tatis Jr. is healthy like he is now, the Padres have a dangerous offense. They are averaging 5.2 runs a game despite playing their first four games at Petco Park. This matchup is at Pacific Bell Park, a pitcher's park, too, but not as anti-offense as Petco Park. The Padres have shown a major improvement this season on working the count and being more patient at the plate. 
I really like San Diego starter Chris Paddack. But he'll be pitching on four day's rest for the first time in his big league career having always gone on five day's rest before. 
Johnny Cueto continues on his comeback trail after tossing just 16 innings last season. So the Giants are likely to bring him along slowly. San Francisco has one of the worst bullpens in the majors.